New York Times columnist Paul Krugman fears that President Donald Trump’s insistent complaints of “voter fraud” are a setup to deny the legitimacy of a Democratic majority in the House should the party win in the midterm elections.

Those who don’t believe such a scenario is possible “haven’t been paying attention,” the Nobel laureate warned. Trump has complained, without evidence, that as many as 5 million people voted illegally in the 2016 presidential election. Hillary Clinton beat Trump in the popular vote by nearly 3 million votes. Trump’s claim, if true, would wipe out that margin and then some.

Trump set up a commission to investigate the votes, but it has not substantiated his claims, nor has it issued any reports. Commission member Matthew Dunlap, Maine’s Democratic secretary of state, said the panel was the “most bizarre thing I’ve ever been a part of.”

Yet Trump keeps raising the issue. Krugman retweeted Trump’s warning Saturday that “all levels of government” are watching out for “VOTER FRAUD” in the upcoming elections.